Thermocouple Converter: mV to Celsius and Celsius to mV Calculator

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Use this thermocouple converter to calculate the relationship between thermocouple voltage and temperature. The calculator supports both conversion directions: Celsius to millivolts and millivolts to Celsius. It works with the common IEC 60584 thermocouple types B, E, J, K, N, R, S, and T.

Thermocouples do not produce a linear signal. Their output voltage changes with temperature according to a polynomial relationship. That is why a proper thermocouple calculator is more accurate than a simple fixed sensitivity value such as 41 microvolts per degree Celsius for Type K. Approximate sensitivity is useful for quick checks, but engineering calculations should use the correct thermocouple reference equations.

What Is a Thermocouple Converter?

A thermocouple converter is a calculation tool that converts thermocouple electromotive force, usually measured in millivolts, into temperature. It can also calculate the expected thermocouple voltage for a known temperature.

The two most common conversions are:

Celsius to mV: used when you want to know the expected thermocouple voltage at a given temperature.
mV to Celsius: used when you have measured thermocouple voltage and want to calculate the corresponding temperature.

For example, a Type K thermocouple produces about 4.096 mV at 100 degrees Celsius. The exact value depends on the official reference polynomial used for the selected thermocouple type.

Supported Thermocouple Types

This thermocouple converter supports the IEC 60584 standard thermocouple types listed below.

Type	Materials	Temperature Range
Type B	Pt30Rh/Pt6Rh	0 to 1820 °C
Type E	NiCr/CuNi	-270 to 1000 °C
Type J	Fe/CuNi	-210 to 1200 °C
Type K	NiCr/NiAl	-270 to 1372 °C
Type N	NiCrSi/NiSiMg	-270 to 1300 °C
Type R	Pt13Rh/Pt	-50 to 1768 °C
Type S	Pt10Rh/Pt	-50 to 1768 °C
Type T	Cu/CuNi	-270 to 400 °C

Each thermocouple type uses different materials, has a different useful temperature range, and produces a different voltage-temperature curve.

How to Use the Thermocouple Converter

Follow these steps to use the calculator:

Select the thermocouple type, such as Type K, Type J, or Type T.
Choose the conversion direction: Celsius to mV or mV to Celsius.
Enter the known value in the input field.
Click Convert.
Read the converted result and check whether the input is inside the valid range.

The result panel also shows the selected thermocouple range and a warning if the entered value is outside the supported range.

Celsius to mV Thermocouple Conversion

When converting Celsius to millivolts, the calculator uses the selected thermocouple reference function. The general equation is:

E = c0 + c1T + c2T² + c3T³ + ... + cnTn

Where:

E is the thermocouple voltage in millivolts.
T is the temperature in degrees Celsius.
c0, c1, c2, and the remaining terms are polynomial coefficients for the selected thermocouple type.

Some thermocouple types use more than one polynomial range. For example, Type K uses different coefficients below and above 0 °C. The calculator automatically selects the correct polynomial range based on the input temperature.

mV to Celsius Thermocouple Conversion

When converting millivolts to Celsius, the calculator uses inverse polynomial equations. The general equation is:

T = d0 + d1E + d2E² + d3E³ + ... + dnEn

Where:

T is the calculated temperature in degrees Celsius.
E is the thermocouple electromotive force in millivolts.
d0, d1, d2, and the remaining terms are inverse polynomial coefficients.

Inverse conversion is useful when a measuring instrument, data acquisition system, or transmitter gives you the thermocouple voltage and you need to calculate the temperature.

Why Thermocouple Type Matters

Different thermocouple types are made from different metal combinations. Because of this, they produce different voltage outputs for the same temperature. A Type K thermocouple and a Type J thermocouple do not generate the same millivolt signal at 100 °C.

Selecting the wrong thermocouple type can cause a large temperature error. Always confirm the sensor type before using a thermocouple conversion table or calculator.

Common Thermocouple Applications

Thermocouples are widely used because they are rugged, affordable, and suitable for a wide temperature range. Common applications include:

Industrial temperature measurement
Furnaces and kilns
Boilers and heat exchangers
Engines and exhaust systems
Laboratory heating equipment
Process control instrumentation
HVAC and refrigeration testing

Type K is one of the most common general-purpose thermocouples. Type J is often used in older industrial systems. Type T is useful for low-temperature work, while Type R, Type S, and Type B are used for high-temperature applications.

Thermocouple Sensitivity

Thermocouple sensitivity is usually expressed in microvolts per degree Celsius. It describes how much the thermocouple voltage changes for each degree of temperature change.

Approximate sensitivities include:

Type	Approximate Sensitivity
Type B	10 µV/°C
Type E	68 µV/°C
Type J	50 µV/°C
Type K	41 µV/°C
Type N	39 µV/°C
Type R	10 µV/°C
Type S	10 µV/°C
Type T	43 µV/°C

These values are only approximate. The actual voltage-temperature relationship is nonlinear, so the calculator uses polynomial equations instead of a single fixed sensitivity value.

Important Note About Cold Junction Compensation

A real thermocouple measurement normally requires cold junction compensation. The thermocouple voltage depends on the temperature difference between the measuring junction and the reference junction.

This calculator converts between thermocouple EMF and temperature using standard reference relationships. In practical measurement systems, cold junction compensation must be handled by the instrument, transmitter, DAQ module, or measurement circuit.

FAQ

What is a thermocouple converter?

A thermocouple converter is a tool that converts thermocouple voltage in millivolts to temperature in degrees Celsius, or converts temperature to the expected thermocouple millivolt output.

How many millivolts does a Type K thermocouple produce at 100 °C?

A Type K thermocouple produces approximately 4.096 mV at 100 °C when calculated using the standard reference polynomial.

Can I use the same equation for all thermocouple types?

No. Each thermocouple type has its own polynomial coefficients. Type B, E, J, K, N, R, S, and T thermocouples all have different voltage-temperature relationships.

Why is thermocouple conversion nonlinear?

Thermocouple voltage is generated by the Seebeck effect, and the relationship between temperature and voltage is not perfectly linear. Polynomial equations are used for accurate conversion.

Does this calculator include cold junction compensation?

The calculator performs standard thermocouple EMF and temperature conversion. Cold junction compensation is a separate measurement requirement that must be handled in real instruments and circuits.